Summer Survival: Understanding Yellowing of Cool-Season Turfgrass and Nurturing Your Lawn through the Heat

The summer heat can be both a blessing and a curse for cool-season turfgrass. While warm temperatures bring rapid growth and lush greenery, they can also present challenges that lead to the dreaded yellowing of your lawn. Seeing your once-vibrant grass turn yellow can be disheartening, but fear not! In this blog post, we’ll delve into the reasons behind the yellowing, explore how soil moisture impacts this phenomenon, and discuss effective ways to help your turfgrass survive and thrive during heat incidences.

Why Does Cool-Season Turfgrass Turn Yellow in the Summer Heat?

Cool-season turfgrass, such as Kentucky bluegrass, perennial ryegrass, and fescue varieties, thrives in mild temperatures. When the summer heat arrives, these grasses face a range of challenges that contribute to their yellowing:

1. Heat Stress: Cool-season grasses are most comfortable in temperatures between 60°F to 75°F. When exposed to prolonged high temperatures above 85°F, they experience heat stress, leading to yellowing and discoloration.
2. Drought Stress: During hot summer days, evapotranspiration increases, causing turfgrass to lose more water than it can absorb. This results in drought stress, as the grass struggles to maintain sufficient moisture levels.
3. Shallow Root Systems: Cool-season grasses typically have shallow root systems compared to their warm-season counterparts. The lack of deep roots makes them more vulnerable to heat and drought stress.
4. Lack of Moisture: Insufficient irrigation or irregular watering practices can lead to dehydration, depriving the grass of the essential moisture it needs to stay healthy and green.
5. Disease Pressure: Prolonged heat and humidity create favorable conditions for disease development, adding further stress to the grass and contributing to yellowing.

The Role of Soil Moisture in Yellowing

Surprisingly, cool-season turfgrass can turn yellow even when there’s adequate soil moisture. This is due to the phenomenon known as “summer dormancy” or “heat-induced dormancy.” When temperatures rise, the grass enters a self-preservation mode, redirecting energy and resources to the root system to survive the heat and conserve water.

During this dormancy, the grass reduces its photosynthetic activity, leading to a decrease in chlorophyll production. Chlorophyll is responsible for the green color in plants, so the reduction in chlorophyll levels causes the grass to turn yellow or straw-colored. This is a natural survival mechanism for the grass, as it conserves energy and resources during stressful conditions.

Ways to Help Your Cool-Season Turfgrass Survive Summer Heat Incidences

While summer dormancy is a natural response, there are several effective strategies to support your turfgrass and minimize yellowing during heat incidences:

1. Adequate and Consistent Irrigation:

• Water deeply and infrequently to encourage deeper root growth.
• Irrigate in the early morning to reduce evaporation and allow the grass to dry before evening, minimizing disease risk.
• Adjust watering schedules based on rainfall and soil moisture levels.

2. Improved Soil Quality:

• Conduct a soil test to assess nutrient deficiencies and pH levels. Amend the soil as necessary to provide the optimal environment for healthy turf growth.

3. Core Aeration:

• Periodically aerate the lawn to relieve soil compaction, allowing for better water and air movement in the root zone.

4. Mulch Grass Clippings:

• Leave grass clippings on the lawn after mowing to provide nutrients and promote soil moisture retention.

5. Fertilize Wisely:

• Apply a slow-release fertilizer tailored to the needs of cool-season grasses. Avoid excessive nitrogen applications, as they can increase growth and stress the grass during hot weather.

6. Shade Management:

• Plant shade trees strategically to provide relief to parts of the lawn during the hottest parts of the day.

7. Regular Mowing and Height Adjustment:

• Mow regularly, ensuring the grass height remains within the recommended range for your specific grass species.
• Avoid scalping the lawn, as it stresses the grass and reduces its ability to withstand heat and drought.

8. Pest and Disease Control:

• Monitor for pests and diseases regularly and take appropriate measures if necessary to prevent additional stress on the grass.

9. Overseeding and Renovation:

• Consider overseeding or renovating the lawn with heat-tolerant cool-season grass varieties to improve its resilience to summer stress.

Conclusion

Understanding the reasons behind the yellowing of cool-season turfgrass during summer heat is the first step towards nurturing your lawn through challenging conditions. Embrace the concept of summer dormancy as a natural survival mechanism, and support your grass with consistent and strategic lawn care practices. By providing adequate soil moisture, improving soil quality, practicing proper irrigation, and incorporating other helpful techniques, you can ensure your turfgrass stays green and healthy, even during the hottest days of summer. Remember, a little TLC goes a long way, and your lawn will thank you with its resilience and vibrant green appearance all year long. Happy lawn nurturing!